Aerosol generator

ABSTRACT

An aerosol generator ( 100 ) has a vibratable plate ( 1 ) with apertures therein and an annular piezo ( 2 ) which causes movement of the vibratable plate ( 1 ). An annular support member ( 3 ) supports the piezo ( 2 ) and the vibratable plate ( 1 ). A first electrical power conducting pin ( 10 ) engages directly with a first, top, surface of the piezo ( 2 ). A second electrical power conducting pin ( 11 ) indirectly conducts electrical power to a second surface of the piezo ( 2 ), by contacting an extension tab ( 103 ) of the support member ( 20 ), also on its top side. There is a film of cured epoxy adhesive on the tab ( 103 ), providing excellent gripping force between the pin ( 11 ) and the support ( 3 ). The aerosol generator ( 100 ) avoids need for soldered joints for electrical contact, and the pins are conveniently mounted parallel to each on the on the same lateral and top side of the piezo and support member. The pins may have multi-point tips ( 50 ) for particularly effective electrical contact.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims the benefit of U.S. ProvisionalApplication No. 61/389,502 filed Oct. 4, 2010 the complete contents ofwhich is incorporated herein by reference.

INTRODUCTION

This invention relates to aerosol generators.

Aerosol generators of the type comprising a vibratable aperturedmembrane, a vibration generator such as a piezo element, and a supportare known. An aerosol generator of this type is illustrated in FIGS. 1and 2. A membrane 201 is supported by a metal washer 203 on top of Whichthere is an annular piezo 202. When the piezo 202 is electricallyexcited it moves in a radial direction as shown by the arrow A. Thiscauses the apertured plate or membrane to move in a vertical directionas shown by the arrow B. This, in turn, causes liquid on the aperturedplate to pass through the holes in the membrane 1 and thus delivering afine mist of aerosol to the underside of the membrane 1.

To electrically excite the piezo 202, electrical power must be conductedto it and connected on each side. Traditionally, this is done bysoldering wires to the conductive surfaces of the vibration generator.The other ends of the wires are soldered to conductive electrical pinswhich are held in a nebulizer housing to receive the female end of adetachable cable. This arrangement is illustrated in FIG. 2, from whichit will be seen that there are four connections 205, 206, 207, and 208.

This method of connection suffers from the disadvantage that the fourconnections must be soldered. Soldering is a labour-intensive operationand does not lend itself to automation.

U.S. Pat. No. 5,435,282 (Haber) also describes a nebulizer. In this casethe membrane is supported by a housing having a downwardly-dependingskirt. The piezo is a discrete element on one side of the housing. Acontact pin contacts the top surface of the piezo and another two pinscontact the underside of the housing.

The invention is directed towards providing an improved aerosolgenerator, which soldered contacts are minimized or eliminated whilealso achieving a simple arrangement of parts.

SUMMARY OF THE INVENTION

According to the invention, there is provided an aerosol generatorcomprising:

a vibratable member having apertures therein;

a vibration generating element, whereby excitation of the vibrationgenerating element causes movement of the vibratable member;

a support member, the vibration generating element and the vibratablemember being mounted to the support member;

a first electrical power conducting pin which engages with a firstsurface: of the vibration generating element;

a second electrical power conducting pin for conducting electrical powerto a second surface of the vibration generating clement;

wherein the vibration generating element and the support member areannular, and

wherein the second surface of the vibration generating element ismounted to the support member, and the second conducting pin engageswith the support member.

In one embodiment, the vibration generating element is mounted to thesupport member by means of an electrically conductive adhesive.

In one embodime east one electrical conducting pin comprises amultipoint contact region.

In one embodiment, there is in the range of 7 to 14 tips in saidmultipoint contact region.

In one embodiment, the support, member includes a substrate and a filmand the second conducting pin contacts said film.

In one embodiment, the film is cured adhesive.

In one embodiment, the adhesive comprises an epoxy.

In one embodiment, the film has a hardness in the range of 70 to 85Shore D.

In one embodiment, the film has a tensile modulus in the range of2,000-7,000 MPa.

In one embodiment, the vibration generating element is secured to thesupport member by an adhesive, and the film is of the same material assaid adhesive.

In one embodiment, the second conducting pin cont Pts an extension tabof the support member.

In one embodiment, the second conducting pin contacts an extension tabof the support member and said film is in the form of a discrete pad onthe extension tab.

In one embodiment, said adhesive is spaced apart ficm adhesive under thevibration generating element.

In one embodiment, said substrate comprises a steel washer.

In one embodiment, each of the conducting pins comprises a spring pin.

In one embodiment, the first and second conducting pins are identical.

In one embodiment, the pins comprise a barrel and a plunger which isbiased by a spring housed in the barrel.

In one embodiment, the spring contact force exerted is in the range of1.3N to 3 N.

In one embodiment, the plunger of the pin is of a material with a lowelectrical resistivity.

In one embodiment, the material of the plunger is selected fromBeryllium Copper alloy, Nickel, Copper Zinc alloy, or Stainless Steel.

In one embodiment, an interfacial contact surface of at least one pinhas a coating thereon to prevent oxidation of the interfacial surfaces.

In one embodiment, the coating comprises a metallic coating.

In one embodiment, the coating comprises an undercoating and an outercoating.

In one embodiment, the undercoating comprises nickel or silver.

In one embodiment, the outer coating comprises gold or nickel.

In one embodiment, the pins are substantially parallel to each other,extending on the same side of the vibration generating element and thesupport member.

In one embodiment, the pins are offset laterally on one side of thesupport member and the vibration generating element.

In one embodiment, the generator further comprises a retainer supportingan assembly of the support member, the vibration generation element, andthe vibratable member; wherein the retainer engages an underside of thesupport member via an annular seal and engages a top surface of thesupport member via a top counter-balancing annular seal.

In one embodiment, the top annular seal is adjacent the edge of thevibratable member and has a smaller radial dimension then the bottomannular seal.

In one embodiment, the bottom annular seal contacts the support memberat a location underneath the vibration generating element, and the topannular seal contacts the support member laterally inside of thevibration generating element.

According to another aspect, the invention provides an aerosol generatorcomprising:

a vibratable member having apertures therein;

a vibration generating element, whereby excitation of the vibrationgenerating element causes movement of the vibratable member;

a support member, the vibration generating element and the vibratablemember being mounted to the support member;

a first electrical power conducting pin which engages with a firstsurface of the vibration generating element;

a second electrical power conducting pin for conducting electrical powerto a second surface of the vibration generating element;

wherein the vibration generating element and the support member areannular, and

wherein the second surface of the vibration generating element ismounted to the support member, and the second conducting pin engageswith the support member, and

wherein at least one electrical conducting pin comprises a multipointcontact region.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood from the followingdescription of an embodiment thereof, given by way of example only, withreference to the accompanying drawings, in which:

FIGS. 1A and 1B are diagrammatic cross sectional views of a prior artaerosol generator, and FIG. 2 is a perspective view of the connection ofthe aerosol generator of FIGS. 1A and 1B to conductive electrical pins;

FIG. 3 is an exploded perspective view of an aerosol enerator accordingto the invention;

FIG. 4 is a cross sectional, of an aerosol generator according to theinvention, including an enlarged view illustrating the core in moredetail;

FIG. 5 is a perspective view showing how pins make solderless contact todrive the piezo, and

FIG. 6 shows conductive adhesive application on a support washer;

FIG. 7 is a perspective of a spring pin;

FIG. 8 is a cross sectional view of the pin of FIG. 7; and

FIG. 9 is a perspectiveew of an alternative spring pin according to theinvention.

DETAILED DESCRIPTION

Referring to FIGS. 3 to 6 of the drawings there is illustrated anaerosol generator 100 according to the invention. The aerosol generatorcomprises a vibratable member such as a vibratable aperture plate 1, avibration generator 2, and a support washer 3. The vibration generator 2in this case comprises an annular piezoelectric element (“piezo”) 2having a first or upper surface and a second or lower surface. The piezo2 is supported by the washer 3. The aperture plate 1 is supported by thesupport washer 3. A braze ring 4 is also provided.

In use, liquid to be aerosolised is received at a first upper surface ofthe aperture plate 1 and the piezo 2 is activated. Aerosolised liquid isgenerated at the second or lower surface of the aperture plate 1 byejecting droplets of liquid upon activation of the piezo 2. Theapertures in the aperture plate 1 are sized to aerosolise the liquidsuch that the majority of the droplets have a size of less than 6micrometers.

The vibratable member could be non planar, and may be dome-shaped ingeometry.

Electrical power is supplied to the piezo 2 in this case by a firstconducting pin 10 and a second conducting pin 11. The first conductingpin 10 is in direct contact with the upper surface of the piezo 2. Thesecond conducting pin 11 is in electrical contact with the upper surfaceof the support washer 3 via conductive adhesive 20 on a tab 103 of thesupport washer 3. The washer 3 and the conductive adhesive 20 are inturn is in electrical contact with the lower surface of the piezo 2.This arrangement is best illustrated in FIGS. 4 to 6.

The support washer 3 in turn engages against a lower O-ring 25 which ishoused in a groove 26 of a support housing 27. The support washer 3 alsoengages against an upper O-ring 28 in the upper part 29 of the mainhousing. The washer 3 is sandwiched between the upper O ring 28 and thelower O ring 25. This subassembly is in turn sandwiched between theupper housing 29 and the lower retainer clip 27. The arrangement of thelower retaining clip 27 provided uniform support around the supportmember 3, counter-balanced by the support forces applied via the O-ring28 and the pins 10 and 11. This helps to achieve consistent operation ofthe aerosol generator 100, with reduced risk of fatigue in the sealbetween the plate 1 and the support washer 2, and a predictable platevibration response to the applied electrical drive.

To accommodate automation low-cost manufacture and consequently greatermanufacturing capacities to supply higher volume market demands, bothspring pins 10, 11 are the same and are placed in the same direction oforientation.

By attaching the piezo 2 to the support washer 3 using an electricallyconductive means, the second spring pin 11 provides electricalcommunication to the underside of the piezo 2 through the top surface ofthe washer 3. The first spring pin 10 provides electrical conductionthrough the top surface of the piezo 2.

In the invention electrical spring pins 10, 11 are used to connectdirectly between the female end of a detachable cable and the electricalsurfaces of the piezoelectric generator 2. No soldering is required andthe use of such pins facilitates assembly by automatic means.

To facilitate greater capacities, and to supply higher volume marketdemands the electrically conductive liquid adhesive 20 is used to attachthe underside of the piezo 2 to the washer 3. This is applied byautomatic means. The viscosity, rheology, application rate, beadthickness, pressure of support washer/piezo contact are optimised tofacilitate application of the conductive liquid adhesive by automaticmeans, both in the annular pattern and as a pad on the tab 103. Suchadhesives may be cured at normal temperature or may require exposure tohigher predetermined temperatures for a preset period of time to form astrong bonding attachment. The optimum bonding attachment is achievedwhen the adhesive is cured to provide optimum strength condition.Epoxies are particularly suited for this application and moreparticularly those with tensile moduli in the range of 300 to 10,000 MPaand more typically in the range of 2,000-7,000 MPa. Such materials haveresistances in the order of 1 milliohm/cm2, but could be higher up to100 milliohm/cm2. Optimum mechanical properties are achieved when suchadhesives are cured in the ranges of 3 minutes at 175 degrees centigradeto 240 minutes at 100 degrees centigrade. Typical hardness are in therange of 70-85 Shore D (ASTM D2240).

The piezo 2 may alternatively be attached to the washer 3 by means ofsoldering by automatic means to provide an electrically conductive pathbetween the top of the washer and the bottom of the piezo 2.

Typically the piezo 2, when electrically excited, vibrates atapproximately, 134 KHz. This presents several problems.

Using the spring pins 10 and 11, the interfacial electrical connectionbetween the spring contact surface and the surface of the support washer3 and the piezo 2, will be in pressure contact rather than mechanicallyconnected together as with soldered joints. To ensure good electricalcontact with spring pressure pins while the assembly vibrates at 134KHz, to aerosolise medication in a corrosive ventilation circuitenvironment, the interfacial connection between the spring pin contactarea and the surface of the washer and piezo are critical. Nebulisersincorporating the aerosol generator of the invention must be able toperform in a wide range of modes of use. Such nebulizers are often usedintermittently over a 28 day period or can be used continuously for upto 7 days.

A number of undesirable mechanisms can occur such as oxidisation,corrosion mechanism, galvanic corrosion, mechanical vibrations, frettingwear to cause loss of electrical contact at the interface.

Referring particularly to FIG. 8, each pin 10, 11 comprises a plunger30, a spring 31 and a barrel 32.

The spring contact force exerted by the spring pin is approximatelybetween 1.3 and 3 Newtons which helps to reduce fretting wear as thereis less pin bounce on the surface.

Choosing pin materials of a low electrical resistivity such as BerylliumCopper alloy (BeCu), Nickel (Ni), or Copper Zinc alloy (CuZn) andstainless steel (SS 303) contributes to increased electricalconductivity. Barrel materials such as copper, brass and bronze alloysexhibit good electrical conductivity as well as good corrosionresistance and mechanical strength and are suitable for thisapplication.

Metallic coatings to prevent oxidisation of the interfacial surfacessuch as Gold (Ag) over Nickel (Ni), also contribute to increasedelectrical conductivity. Coatings of 1-3 microns of gold over 3 micronsof Nickel undercoat are particularly suitable. Spring parent materialscan consist of Music Wire (ASTM A 228) and 304 Stainless Steel. Metalliccoatings such as 0.05microns of Gold over a 0.05 micron Nickel undercoatare especially suitable

‘Constriction’ of the electrical current at the electrical interfaceincreases the contact electrical resistance and can cause an undesirablerise in temperature. The total effective area of electrical contactneeds to be made as large as possible to help create and maintainacceptable quality of electrical connection.

A conventional semi-hemispherical pin head has the disadvantage of notbeing able to expose new effective contacting surfaces.

A vibrating multipoint contact pin head 50 as illustrated in FIG. 9 hasthe considerable advantage of being able to mechanically expose newareas for good electrical connection thus breaking down any oxidisationlayers which can cause an insulation barrier. The multipoint contact pinincreases the potential electrical contact surface area. The increasednumber of contact points, (which can vary in some embodiments from 7-14)act as a fail safe, if one contact becomes compromised the othercontacts will form the required electrical contact. Additionally, theaddition of the multi-points rather than a semi-hemispherical or flatcontacting spring pin surface increases the specific force at theseinterfacial points, reducing the potential for undesirable frettingwear, and causing the multi-points to engage new micro surfaces. FIG. 10shows another multi-point head 60 having seven points 61, with a V anglebetween of 55°, giving a point angle of 62.5°.

It has been found that a combination of the multi-point conducting pinand the film of cured adhesive provide particularly good reliability ofcontact. The points or tips penetrate the film to a greater extent thanthey would the underlying material of the (steel) support member 3. Thisallows an optimum combination, in which the steel of the support memberprovides excellent rigidity for supporting the apertured membrane 1 andthe piezo 2, while at the same time the film 20 part of the supportmember allows excellent electrical contact despite the harshenvironment, in which the nebulizer may be operating for a prolongedperiod.

Furthermore, the retainer and sealing arrangement also contribute to theabove features to help ensure reliable operation. The retainer 27 andO-ring 25 provide comprehensive and uniform support directly below thepiezo 2, while the smaller-diameter O-ring 28 transmits support forcesfrom above closer to the circumference of the membrane 1 where it issupported by the support member 3.

As the aperture plate 1 is attached to the support washer 3 by a thermalmeans such as by brazing, the elevated temperatures to effect a goodjoint bond can have an undesirable effect on any plating applied to thewasher 3, which is typically Stainless Steel or Hastelloy. It is notpossible to apply plating afterwards as it is difficult to mask off theaperture plate to prevent the ingress of conductive plating materialssuch as silver, gold, nickel or such like into the apertures.

One way of overcoming this is to apply a conductive adhesive similar tothe adhesive 20 that bonds the piezo 2 to the support washer 3. This canbe applied by automatic means as part of the process of application toattach the piezo 2. It is not required on top of the piezo 2 to maintainconductivity with the spring pin 10 as such elements are typicallysilver coated.

A particular current and voltage is required to drive the nebulizer 100at the desired frequency to generate the optimum aerosol range [2.5-6.5μm particle size and flow rates between 0.1 and 2 ml/min] Voltages aretypically 12V and the nebulizer is driven at 128 kHz. The multi-pointedspring pin 50 makes excellent electrical contact with the piezo 2 andthe washer 3, achieving a uniform performance in which an aerosol plumehas the desired characteristics of particle size and flow rate.

Because the piezo is annular it ensures uniform radial vibration, whichallows the core to work at its optimum mode of vibration. Thissymmetrical arrangement allows the aperture plate to move perpendicularto the piezo in a uniform and consistent manner, with a uniform forcesapplied around its circumference. Importantly, the pins do not interferewith the mode of vibration. Their springs act as dampeners which ensurethat these electrical connectors do not impact on the core's naturalfrequency. They add additional mass through a normal reaction to thecore's movement, this normal reaction being absorbed via the pogo pinspring.

Also, it will be appreciated that the arrangement of the invention onlyrequires two holding posts.

Because the pin 11 has conductive glue between itself and the main bodyof the support washer 3, fretting and resulting intermittency issues areavoided, and there is improved electrical connection. The use of aconductive glue reduces the potential of increased contact resistancewhich is a known indicator to electrical contact fatigue. Also, the useof multiple contact points 50 increases the potential electrical contactarea.

The maintenance of electrical conductivity throughout the service lifeof the nebulizer is accomplished by the following features

-   Pin contacting forces greater than 1.3N@1 mm deflection-   Materials selected with low electrical resistivity-   Less oxidising materials plated on to spring pin contacting surfaces-   Spring pin head geometry selected so as to provide multipoint    connecting points to the mating surface-   Spring head geometry selected so as to expose new surfaces to better    electrical connection.

Also, it will be appreciated that the invention is used in themanufacture of aerosol generators which require electrical connectionwhich have demanding requirements and which are required to bemanufactured in high volumes without the use of laborious handsoldering.

The invention is not limited to the embodiments hereinbefore described,with reference to the accompanying drawings, which may be varied inconstruction and detail. For example, there may be a film of a materialsuch as that of the film 20 on the piezo, for contact with the firstconducting pin.

1-31. (canceled)
 32. An aerosol generator comprising: a vibratablemember having apertures therein; a vibration generating element; asupport, the vibration generating element and the vibratable memberbeing mounted to the support, wherein the support is generally annularand includes a pair of diametrically opposed radially extending tabs; afirst electrical power conducting pin having an end electrically coupledwith the vibration generating element; and a second electrical powerconducting pin having an end electrically coupled with the vibrationgenerating element.
 33. The aerosol generator of claim 32, wherein thesecond power conducting pin is coupled to one of the tabs of the pair oftabs.
 34. The aerosol generator of claim 32, wherein the tabs arecontinuous with the support.
 35. The aerosol generator of claim 32,wherein a conductive coating is positioned on only one tab of the pairof tabs.
 36. The aerosol generator of claim 35, further including a ringof conductive adhesive on the support, wherein the conductive coatingand the conductive adhesive comprise a common material.
 37. The aerosolgenerator of claim 36, wherein the ring of conductive adhesive isdiscrete from the conductive coating.
 38. The aerosol generator of claim32, wherein the support includes a first side and a second side oppositethe first side, wherein each of the vibratable member and vibrationgenerating element are positioned on the first side of the support. 39.The aerosol generator of claim 38, wherein the first side of the supportis an upstream side of the support.
 40. The aerosol generator of claim38, wherein a periphery of the vibratable member is coupled to the firstside of the support.
 41. An aerosol generator comprising: a vibratablemember having apertures therein; a vibration generating element; asupport washer including a main body portion having an adhesive thereon,the support washer further including a radially extending tab, whereinthe tab includes a coating thereon, wherein the adhesive and the coatingare a same material; a first electrical power conducting pin having anend electrically coupled with the vibration generating element; and asecond electrical power conducting pin having an end electricallycoupled with the vibration generating element via the coating.
 42. Theaerosol generator of claim 41, wherein the adhesive and the coating areconductive.
 43. The aerosol generator of claim 41, wherein the adhesiveis discrete and spaced from the coating.
 44. The aerosol generator ofclaim 41, wherein the tab is a first tab, and wherein the support washerfurther includes a second tab, wherein the second tab is free from acoating thereon.
 45. The aerosol generator of claim 41, wherein thesupport washer includes a first side and a second side opposite thefirst side, wherein each of the vibratable member and vibrationgenerating element are positioned on the first side of the washer. 46.The aerosol generator of claim 45, wherein the first side of the supportwasher is an upstream side.
 47. An aerosol generator comprising: avibratable member having apertures therein; a vibration generatingelement having a first surface and a second surface; a support having afirst side and a second side, the second surface of the vibrationgenerating element and the vibratable member being mounted to the firstside of the support, wherein the support is generally annular andincludes at least one radially extending tab; a first electrical powerconducting pin having an end electrically coupled with the first surfaceof the vibration generating element; and a second electrical powerconducting pin having an end electrically coupled with the secondsurface of the vibration generating element via the at least one tab.48. The aerosol generator of claim 47, wherein the first side of thesupport is an upstream side of the support, and wherein the secondsurface of the vibration generating element is a downstream surface ofthe vibration generating element.
 49. The aerosol generator of claim 47,wherein the at least one tab is continuous with the support.
 50. Theaerosol generator of claim 47, further including a conductive adhesiveon the first side of the support and a conductive coating on the atleast one tab.
 51. The aerosol generator of claim 50, wherein theconductive adhesive and the conductive coating comprise a commonmaterial.